The present invention is directed to novel amine functional silanes having improved thermal stability for use in filled polymer composites, and intermediates for producing certain of the novel silanes. More paticularly, the invention relates to ethylene bridged benzylamine derivatives and their use in improving the mechanical properties of polymer composites which are processed at high temperatures or are continuously exposed to high temperatures.
Commercially available silanes, which are conventionally used as coupling agents for polymers filled or reinforced with glass fibers or the like are aliphatic compounds having an amine functional group. Examples of such compounds are 3-aminopropyltriethoxysilane and 3-[2-aminoethyl(aminopropyl)]trimethoxysilane. While these silanes have demonstrated sufficient thermal stability for use with the most common filled resins, the introduction of resins which process in excess of 350.degree. C. or receive continuous exposure to temperatures in excess of 150.degree. C. has made it desirable to produce silane adhesion promoters with greater thermal stability than the aliphatic amine silanes whose thermal stability is insufficient to withstand the above temperatures.
The general order of thermal stability for organosilane coupling agents is shown below:
______________________________________ ZCH.sub.2 CH.sub.2SiX.sub.3 ZCH.sub.2SiX.sub.3 ZCH.sub.2 CH.sub.2 CH.sub.2SiX.sub.3 ZCH.sub.2PhSiX.sub.3 beta substitution alpha substitution gamma substitution aromatic substitution ##STR1## ______________________________________
In the above formulas Z is a functional group intended to be reactive with the polymer portion of a composite, and X is a hydrolyzable group, typically alkoxy, which is displaced during the reaction with the substrate portion of a composite. The conventional aliphatic silane coupling agents referred to above are of the gamma substitution type.
It has been demonstrated that silane coupling agents having considerable thermal stability can be prepared when aromatic groups are bound to the silicon. Wholly aromatic compounds such as aminophenyltriethoxysilane have been reported as having excellent adhesion promotion properties in polymer composites. However, aromatic silanes have not been commercially attractive due to the adverse economics associated with the multi-step syntheses and low yield production of these aromatic silanes.
Recently, a new class of silanes has been developed which incorporates an aliphatic bridge between the aromatic group and the silicon atom. While the thermal stability of these new silanes is not as great as that of the purely aromatic compounds, the thermal stability is significantly greater than the conventionally used gamma functional silanes. Even though an aliphatic bridge segment is present in these compounds, the thermal stability closely resembles that of the aromatic analogs and is only marginally lower. This is surprising since the ethylene bridge plus the methylene group on the functional side of the phenyl group amounts to the same number of methylene groups as in the aliphatic gamma substituted silanes. Ethylene bridged aromatic silanes previously made include (chloromethyl) phenylethyltrimethoxysilane (ClCH.sub.2 --Ph--CH.sub.2 CH.sub.2 Si(OCH.sub.3).sub.3) and styrylethyltrimethoxysilane (H.sub.2 C.dbd.CH--Ph--CH.sub.2 CH.sub.2 Si(OCH.sub.3).sub.3).